One of the main concerns that a fork truck operator has is the visibility available to him when operating his fork truck in the direction of the forks extension. Another concern of owners of fork truck mechanisms is the cost of replacement and repair of hydraulic hoses. The conventional fork truck having multiple stage lifting mechanisms to lift loads beyond approximately 8 feet as are well known in the art, have a considerable number of hoses extending from a hydraulic reservoir or pump to each and every individual cylinder requiring hydraulic fluid. By extending the hose the distance between the reservoir and the respective hydraulic cylinders and further by allowing the hose to extend through at least two passes to allow for movement of the stages of the carriage mechanism, a considerable amount of hose is required. The hydraulic hose normally passes from the cylinder over a pulley down to another pulley up to another pulley and then down finally to the reservoir as an example. This hose coupled with the chain conventionally found in driving multiple stage lifting mechanisms tends to block the operators view in between the carriages and creates a maintenance problem for the operator of the fork truck.
Canadian Pat. No. 1,097,266 addresses such a problem wherein the hose extends from one cylinder around the carriage to the other free lift cylinder wherein the hose will not block the view of the operator, however, there still remains the problem of maintaining the hose. Such a construction as embodied in FIG. 12 of the Canadian Pat. No. 1,097,266 describes the known construction to convey fluid from one cylinder to another cylinder.
U.S. Pat. No. 4,018,307 describes a tri-pack of cylinders which are mechanically and hydraulically interconnected wherein the hydraulic fluid admitted to the interior of a secondary cylinder passes through a hydraulic interconnection between the cylinders to a pair of continuously disposed primary cylinders. This is best illustrated in relation to FIGS. 3 and 6. Thus, a fitting illustrated in FIG. 7 of the 4,018,307 patent is provided to allow for the interconnection of the cylinders, but the cylinders are constructed in conventional manner. There is no outlet from the top of the cylinder to allow fluid to pass through the hollow of the piston and be used as not only a driving means but as well as a fluid conducting means.
Canadian Pat. No. 1,174,205 describes a cylinder used in a multiple stage assembly having two piston rods extending away from one another in use as described in relation to FIG. 5. Again, the fluid does not pass through the piston rod and the piston does not behave as a conducting channel for hydraulic fluid.
Canadian Pat. No. 1,220,404 describes and as illustrated in FIG. 1 a double acting cylinder which is not hollow but merely acts in both directions according to the pressure differentials of fluid flow. This device corresponds to U.S. Pat. No. 4,561,342 and is used as a leveling device for the bucket of a tractor type mechanism.
Soviet Union Publication 645930 describes two-way telescopic power cylinder having a hollow rod with channels therein as illustrated in the figure, but having no passage of fluid outside of this cylinder. The fluid will flow through the inlet 9 through to the hollow piston rod 19 and then to a pressure balancing chamber disposed within the assembly. Nowhere within the structure is described the passage of the fluid as best understood by Applicant outside the cylinder. Further, Soviet Union Pat. No. 1158408 describes a hollow piston rod disposed within a cylinder used to transport fluid to all of the nested cylinders within a dump truck mechanism. The dump truck includes a telescoping cylinder which has various number of stages wherein the fluid will pass to all the stages through the hollow piston rod. However, the fluid does not pass outside of the cylinder as not used as conducting means to provide fluid to another cylinder.
Nowhere within the prior art is there found a cylinder used in a material handling truck which has a hollow passage extending therethrough and has inlet and outlet ports to allow the fluid to enter and exit the cylinder wherein the cylinder acts as a normal cylinder in use and further acts as a fluid conducting mechanism.
It is therefore an object of the invention to provide a cylinder constructed for use in a material handling truck, wherein the cylinder behaves as a conventional cylinder but allows for fluid to pass therethrough to locations remote the cylinder.
It is a further object of the invention to reduce the maintenance cost of hoses found in material handling trucks.
Further and other objects of the invention will become apparent to a man skilled in the art when considering the following summary of the invention and the more detail description of the preferred embodiments illustrated herein.